1. Field of the Invention
The present invention relates to circuit interrupters generally and, more specifically, to those kinds of circuit interrupters having a trip mechanism including an automatic trip assembly for generating a magnetically-induced tripping operation.
2. Description of the Prior Art
Molded case circuit breakers and interrupters are well known in the art as exemplified by U.S. Pat. No. 4,503,408 issued Mar. 5, 1985, to Mrenna et al., and U.S. Pat. No. 5,910,760 issued Jun. 8, 1999 to Malingowski, et al., each of which is assigned to the assignee of the present application and incorporated herein by reference.
Circuit interrupters advantageously provide for automatic circuit interruption (opening of the contacts) when an overcurrent condition is determined to exist. One way of determining whether or not an overcurrent condition exists is to provide a trip mechanism with an automatic trip assembly that reacts to a magnetic field generated by the overcurrent condition. In such circuit interrupters, the reaction to the magnetic field is often in the form of a movement of an armature that, in turn, sets in motion a tripping operation. The movement of the armature normally is either away from or towards a magnetic structure from which the magnetic field emanates, and may be influenced by a member(s) which biases the armature away from the magnetic structure. The magnetic structure is connected to an electrical terminal of the conductor from which electrical current is received.
In the prior art, compression springs have sometimes been implemented in the automatic trip assembly in order to provide the aforementioned biasing of the armature away from the magnetic structure. Unfortunately, in order to adjust the predetermined current level that causes this magnetic tripping operation, a different sized compression spring must be used in the prior art in order to provide a different biasing force. It would be advantageous if a way existed by which to provide armature biasing that enabled the biasing level to be adjusted in an easier and more time-efficient manner.
The present invention provides a circuit interrupter that meets all of the above-identified needs.
In accordance with the present invention, a circuit interrupter is provided which includes a housing, separable main contacts disposed in the housing, and an operating mechanism disposed in the housing and interconnected with the contacts. Also provided is a trip mechanism disposed in the housing and having an automatic trip assembly that generates a tripping operation to cause the operating mechanism to open the contacts upon a predetermined current threshold. The automatic trip assembly includes a magnetic yoke, an armature, and a plurality of abutment members. The magnetic yoke has pivot supports providing for a rotatable disposition of a head portion of the armature. The assembly also includes a biasing member having a first portion and a second portion, the first portion abutted against a selected one of the plurality of abutment members, the second portion abutted against the armature and applying a force to the armature in a direction to normally rotationally displace a bottom portion of the armature away from the magnetic yoke, wherein selecting a different one of the plurality of abutment members to be the selected one causes the force to vary.
This and other objects and advantages of the present invention will become apparent from a reading of the following description of the preferred embodiment taken in connection with the attached drawings.